Originally Posted by
Rater202
Some works depict vampires as requiring very little blood and/or being able to subsist off of animals or reserved blood that is no longer viable for transfusion without issue.
Beyond that, depending on the dietary needs of the vampire in question compared to their average power level and the temperament, desires, and goals thereof it's possible that a given vampire could do more good overall than the harm they do.
For an arbitrary example, I pulled out of my ass just now, if a given vampire only needs to kill one human every couple of years and thus has thus luxury to only target serial killers and the like and do proper investigation to make sure that they get the right guy.